Capacitive micromachined ultrasonic transducers with increased lifetime

Abstract

An array of CMUT cells (10) has a DC bias voltage (VB) coupled to the top electrodes of the cells to bias the electrode to a desired collapsed or partially collapsed state. Fuses (200) are coupled in series with the bottom electrodes (22) of the cells which will open and isolate an individual cell from the other still-functional cells of the array in the event of a failure of the individual cell. In a preferred embodiment the cells are coupled to control integrated circuitry such as microbeamformer circuitry and the fuses are formed of semiconductor materials with the integrated circuitry, thereby leaving the MUT surface area available for high density MUT fabrication. Damage to the integrated circuitry due to short-circuiting of the DC bias current through a failed cell is prevented.

The invention claimed is: 
     
       1. A micromachined ultrasonic transducer (MUT) array which is protected from an overcurrent condition comprising:
 a substrate; 
 a plurality of MUT cells formed on the substrate, each cell having a membrane comprising a top electrode and a bottom electrode coupled to the substrate, 
 wherein the plurality of MUT cells comprises a single, common electrode arranged to be coupled to a common reference potential and a plurality of signal electrodes arranged to individually be coupled to an a.c. drive signal, wherein the common electrode comprises the top electrodes of the plurality of MUT cells and each of the plurality of signal electrodes comprises a respective one of the bottom electrodes of the plurality of MUT cells; and 
 wherein each MUT cell further comprises one fuse coupled to a respective signal electrode of the plurality of signal electrodes, wherein the fuse is arranged to open in an event of an overcurrent condition of the MUT cell from the a.c. drive signal to isolate the MUT cell from the other MUT cells of the array. 
 
     
     
       2. The micromachined ultrasonic transducer (MUT) array of  claim 1 , wherein each fuse is coupled in series with the bottom electrode of a MUT cell. 
     
     
       3. The micromachined ultrasonic transducer (MUT) array of  claim 1 , wherein each fuse further comprises a fuse, which is arranged to open through heating or electro-migration. 
     
     
       4. The micromachined ultrasonic transducer (MUT) array of  claim 1 , further comprising:
 an integrated circuit coupled to the MUT array to control operation of the MUT cells, 
 wherein the fuses are located on the integrated circuit. 
 
     
     
       5. The micromachined ultrasonic transducer (MUT) array of  claim 4 , wherein the integrated circuit further comprises an application specific integrated circuit (ASIC). 
     
     
       6. The micromachined ultrasonic transducer (MUT) array of  claim 5 , wherein the ASIC further comprises a substrate, separate from the MUT substrate, with the integrated circuit formed on the substrate,
 wherein the integrated circuit is electrically coupled to the MUT cells to control operation of the MUT cells. 
 
     
     
       7. The micromachined ultrasonic transducer (MUT) array of  claim 6 , wherein integrated circuit and its substrate are bonded to the MUT substrate. 
     
     
       8. The micromachined ultrasonic transducer (MUT) array of  claim 6 , wherein the ASIC further comprises a microbeamformer. 
     
     
       9. The micromachined ultrasonic transducer (MUT) array of  claim 5 , wherein the ASIC further comprises integrated circuitry, formed on the MUT substrate, the integrated circuitry electrically coupled to the MUT array to control operation of the array. 
     
     
       10. The micromachined ultrasonic transducer (MUT) array of  claim 9 , wherein the fuses are formed on the substrate with the integrated circuitry. 
     
     
       11. The micromachined ultrasonic transducer (MUT) array of  claim 10 , wherein the fuses are further formed on the substrate with the integrated circuitry with semiconductor materials. 
     
     
       12. The micromachined ultrasonic transducer (MUT) array of  claim 11 , wherein the semiconductor materials further comprises an integrated circuit metal layer or a polysilicon layer. 
     
     
       13. The micromachined ultrasonic transducer (MUT) array of  claim 12 , wherein the fuses further comprise narrowed traces of semiconductor material. 
     
     
       14. The micromachined ultrasonic transducer (MUT) array of  claim 11 , wherein the fuses further comprise vias of a predetermined dimension. 
     
     
       15. The micromachined ultrasonic transducer (MUT) array of  claim 9 , wherein the ASIC further comprises a microbeamformer. 
     
     
       16. The micromachined ultrasonic transducer (MUT) array of  claim 1 , wherein the top electrodes of the plurality of MUT cell are interconnected. 
     
     
       17. The micromachined ultrasonic transducer (MUT) array of  claim 16 , wherein the common reference potential comprises a ground potential, and wherein the plurality of signal electrodes is arranged to be coupled to both a D.C. reference potential and the a.c. drive signal.